U.S. patent application number 14/065470 was filed with the patent office on 2014-05-01 for calibrating a lighting device comprising a semiconductor light source.
This patent application is currently assigned to OSRAM GmbH. The applicant listed for this patent is OSRAM GmbH. Invention is credited to Andreas Biebersdorf.
Application Number | 20140117994 14/065470 |
Document ID | / |
Family ID | 50479706 |
Filed Date | 2014-05-01 |
United States Patent
Application |
20140117994 |
Kind Code |
A1 |
Biebersdorf; Andreas |
May 1, 2014 |
CALIBRATING A LIGHTING DEVICE COMPRISING A SEMICONDUCTOR LIGHT
SOURCE
Abstract
In various embodiments, a method for calibrating a lighting
device is provided. The lighting device may include at least one
semiconductor light source. The method may include: determining a
thermal power loss of the at least one semiconductor light source;
determining an electrical power of the at least one semiconductor
light source; and determining a light power of the at least one
semiconductor light source from the electrical power and the
thermal power loss.
Inventors: |
Biebersdorf; Andreas;
(Regensburg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OSRAM GmbH |
Muenchen |
|
DE |
|
|
Assignee: |
OSRAM GmbH
Muenchen
DE
|
Family ID: |
50479706 |
Appl. No.: |
14/065470 |
Filed: |
October 29, 2013 |
Current U.S.
Class: |
324/414 |
Current CPC
Class: |
H05B 45/24 20200101;
H05B 45/28 20200101 |
Class at
Publication: |
324/414 |
International
Class: |
G01R 31/44 20060101
G01R031/44 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 2012 |
DE |
10 2012 219 876.8 |
Claims
1. A method for calibrating a lighting device, the lighting device
comprising at least one semiconductor light source, the method
comprising: determining a thermal power loss of the at least one
semiconductor light source; determining an electrical power of the
at least one semiconductor light source; and determining a light
power of the at least one semiconductor light source from the
electrical power and the thermal power loss.
2. The method of claim 1, wherein determining the thermal power
loss comprises determining a temperature difference between a
temperature at the beginning of operation of the lighting device
and a temperature in thermally settled operation of the lighting
device.
3. The method of claim 1, wherein a predetermined thermal
resistance is used for determining the thermal power loss.
4. The method of claim 1, wherein a thermal resistance is
determined in situ for determining the thermal power loss.
5. The method of claim 1, wherein determining the electrical power
comprises determining at least one of a voltage applied to the at
least one semiconductor light source for the operation thereof or
an electric current through the at least one semiconductor light
source.
6. The method of claim 1, wherein determining the light power
comprises forming a difference between the thermal power loss and
the electrical power.
7. The method of claim 1, wherein determining the light power is
followed by varying the electrical power for setting the light
power to a predetermined value or range of values.
8. The method of claim 1, wherein the method is carried out for a
plurality of groups of semiconductor light sources.
9. The method of claim 8, wherein the method is carried out for a
plurality of groups of semiconductor light sources of different
colors.
10. A lighting device, comprising: at least one semiconductor light
source; a voltage measuring device; and a temperature measuring
device; wherein the lighting device is configured to carry out a
method for calibrating the lighting device, the method comprising:
determining a thermal power loss of the at least one semiconductor
light source; determining an electrical power of the at least one
semiconductor light source; and determining a light power of the at
least one semiconductor light source from the electrical power and
the thermal power loss.
11. The lighting device of claim 10, wherein the lighting device is
configured to independently carry out the method; the lighting
device further comprising a correspondingly designed electronic
control unit.
12. A system, comprising: at least one lighting device, comprising:
at least one semiconductor light source; a voltage measuring
device; and a temperature measuring device; wherein the lighting
device is configured to carry out a method for calibrating the
lighting device, the method comprising: determining a thermal power
loss of the at least one semiconductor light source; determining an
electrical power of the at least one semiconductor light source;
and determining a light power of the at least one semiconductor
light source from the electrical power and the thermal power loss;
an external control device; wherein the system is configured to
carry out the method in a distributed manner with respect to said
system.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to German Patent
Application Ser. No. 10 2012 219 876.8, which was filed Oct. 30,
2012, and is incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0002] Various embodiments relate generally to a method for
calibrating a lighting device including at least one semiconductor
light source. Various embodiments also relate to a lighting device
including at least one semiconductor light source, wherein the
lighting device is designed for independently carrying out the
method. Various embodiments are applicable e.g. to LED lighting
devices, e.g. LED lamps and LED modules.
BACKGROUND
[0003] If, for the purpose of generating light, the intention is to
use light emitting diodes (LEDs) which emit light of different
colors (e.g. RGB, "Brilliant Mix" from Osram Opto Semiconductors
and much more), the respective brightnesses have to be well
coordinated with one another in order to achieve a specific
cumulative color locus of the mixed light from the differently
colored light. This coordination changes with temperature
(different temperature response of the LEDs) and with time
(different ageing of the LEDs). The ageing, in particular, cannot
be predicted during production.
[0004] Lighting devices of the relevant type are known which do not
provide closed-loop control of the brightnesses of the LEDs, with
the result that an appreciable change in the cumulative color locus
is accepted in the case of these lighting devices. This is
disadvantageous in particular when a plurality of such lighting
devices are arranged alongside one another, since the human eye can
clearly perceive even just slight color deviations.
[0005] Lighting devices of the relevant type are also known which
have closed-loop control, in which a temperature of the LEDs is
measured and corrected with known or estimated temperature
dependencies.
[0006] Optionally, a predefined (but not necessarily realistic)
ageing behavior can be corrected, e.g. by means of a corresponding
characteristic curve of the power to be impressed over the
operating period. Such lighting devices have the disadvantage that
their correction or calibration of the brightnesses can deviate in
some instances considerably from the actually required correction
in the real installation situation present.
[0007] Moreover, lighting devices of the relevant type are known
which carry out closed-loop control or calibration with the aid of
a color sensor or brightness sensor: in this case, the light
intensity for each color component is measured and correspondingly
corrected. This variant hitherto has been the only one which can
reliably bring about the desired color locus. However, the at least
one sensor required for this is expensive, and, moreover, ageing of
the sensor is an unknown fault source.
SUMMARY
[0008] In various embodiments, a method for calibrating a lighting
device is provided. The lighting device may include at least one
semiconductor light source. The method may include: determining a
thermal power loss of the at least one semiconductor light source;
determining an electrical power of the at least one semiconductor
light source; and determining a light power of the at least one
semiconductor light source from the electrical power and the
thermal power loss.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The above-described properties, features and advantages of
this invention and the way in which they are achieved will become
clearer and more clearly understandable in connection with the
following schematic description of an embodiment explained in
greater detail in association with a drawing.
[0010] The FIGURE shows a lighting device in accordance with
various embodiments.
DESCRIPTION
[0011] The following detailed description refers to the
accompanying drawings that show, by way of illustration, specific
details and embodiments in which the invention may be
practiced.
[0012] The word "exemplary" is used herein to mean "serving as an
example, instance, or illustration". Any embodiment or design
described herein as "exemplary" is not necessarily to be construed
as preferred or advantageous over other embodiments or designs.
[0013] The word "over" used with regards to a deposited material
formed "over" a side or surface, may be used herein to mean that
the deposited material may be formed "directly on", e.g. in direct
contact with, the implied side or surface. The word "over" used
with regards to a deposited material formed "over" a side or
surface, may be used herein to mean that the deposited material may
be formed "indirectly on" the implied side or surface with one or
more additional layers being arranged between the implied side or
surface and the deposited material.
[0014] Various embodiments may at least partly overcome the
disadvantages of the prior art.
[0015] Various embodiments provide a method for calibrating a
lighting device, including at least one semiconductor light source,
wherein the method includes at least the following steps:
determining a thermal power loss, Pth, of the at least one
semiconductor light source; determining an electrical power, Pe, of
the at least one semiconductor light source; and determining a
light power, Pl, of the at least one semiconductor light source
from the electrical power and the thermal power loss.
[0016] This method may have the advantage that it enables a precise
and nevertheless inexpensively implementable stabilization of a
color locus and/or light power or brightness of the at least one
semiconductor light source. In various embodiments, on the one hand
it is possible to dispense with a color sensor, and on the other
hand it is possible to achieve a more precise determination of an
actual light power than just in the case of a temperature
determination. As a result, in particular, an age-dependent change,
e.g. degradation, of the light power can also be determined
sufficiently precisely and if desired corrected in a simple
manner.
[0017] Calibration may be understood to mean, in particular,
reliably reproducible measurement for ascertaining a deviation of a
measured value of a parameter (e.g. light power or brightness) with
respect to a desired value or normal value of said parameter. The
calibration may optionally include taking account of the deviation
during subsequent operation of the lighting device, in particular
by correcting the measured values to the desired value. The method
may also simply be designated as a method for operating a lighting
device.
[0018] In various embodiments, the at least one semiconductor light
source includes at least one light emitting diode. In the event of
a plurality of light emitting diodes being present, they may emit
light in the same color or in different colors. A color may be
monochromatic (e.g. red, green, blue, etc.) or multichromatic (e.g.
white). The light emitted by the at least one light emitting diode
may also be infrared light (IR LED) or ultraviolet light (UV LED).
A plurality of light emitting diodes may generate a mixed light;
e.g. a white mixed light. The at least one light emitting diode may
contain at least one wavelength-converting phosphor (conversion
LED). The phosphor may alternatively or additionally be arranged in
a manner remote from the light emitting diode ("Remote Phosphor").
The at least one light emitting diode may be present in the form of
at least one individually housed light emitting diode or in the
form of at least one LED chip. A plurality of LED chips may be
mounted on a common substrate ("Submount"). The at least one light
emitting diode may be equipped with at least one dedicated and/or
common optical unit for beam guiding, e.g. at least one Fresnel
lens, collimator, and so on. Instead or in addition to inorganic
light emitting diodes, e.g. on the basis of InGaN or AlInGaP,
generally organic LEDs (OLEDs, e.g. polymer OLEDs) may also be
used. Alternatively, the at least one semiconductor light source
may include e.g. at least one diode laser.
[0019] The thermal power loss Pth may be understood to mean, in
various embodiments, that power which is generated or emitted in
the form of heat during operation of the at least one semiconductor
light source.
[0020] The electrical power Pe of the at least one semiconductor
light source may be, in various embodiments, an impressed
electrical power for the at least one semiconductor light
source.
[0021] In one configuration, determining the light power Pl
includes forming a difference between the electrical power Pe and
the thermal power loss Pth. As a result, the light power Pl may be
determined in a particularly simple manner.
[0022] In one development, the light power Pl is determined with
the aid of the relationship
Pl=Pe-Pth (1)
[0023] If, by way of example, the thermal power loss Pth is 60% of
the impressed electrical power Pe, according to equation (1) this
corresponds to a light power of 40% of the electrical power Pe.
[0024] In one configuration, determining the thermal power loss Pth
includes determining a temperature difference .DELTA.T between a
temperature T0 at the beginning of operation of the lighting device
("switch-on instant") and a temperature Tb in a thermally settled
state of the lighting device ("thermalization"), e.g. in accordance
with .DELTA.T=Tb-T0. In thermally settled operation of the lighting
device, a temperature T at the semiconductor light sources may not
or no longer significantly rise. As a result, using the thermal
resistance Rth it is possible to determine the thermal power loss
Pth, e.g. in accordance with
Pth=.DELTA.T/Rth. (2)
[0025] It can take e.g. a few minutes to reach the thermally
settled state.
[0026] In a further configuration, a, e.g. experimentally,
predetermined thermal resistance Rth is used for determining the
thermal power loss Pth.
[0027] In yet another configuration, a thermal resistance Rth is
determined in situ (e.g. during operation of the installed lighting
device) for determining the thermal power loss Pth. This affords
the advantage that in the case of the thermal resistance, an
installation situation of the lighting device, e.g. the ambient
temperature thereof, can be concomitantly taken into account. The
determination in situ can be carried out for example by means of
measurements at slightly different predefined operating currents of
the lighting device.
[0028] In a development that is advantageous for further increasing
a precision with which the thermal power loss Pth is determined, it
is purged of any influence of a thermal power loss of an electronic
unit possibly present. This may be advantageous e.g. if the
electronic unit can influence a temperature measurement for the at
least one semiconductor light source. This may be the case, for
example, if the at least one semiconductor light source and also
the electronic unit are connected to a common heat sink (e.g. a
cooling body) on which a temperature measurement is also carried
out.
[0029] In various embodiments, the thermal power loss of the
electronic unit is determined from its electrical power. In various
embodiments, the thermal power loss of the electronic unit may be
equated with its electrical power since generally only heat is
generated by the electronic unit during its operation.
[0030] The electrical power of the electronic unit may be
predetermined or determined in situ during operation.
[0031] In one configuration, furthermore, determining the
electrical power Pe includes determining a voltage U applied to the
at least one semiconductor light source for the operation thereof
and/or an electric current I through the at least one semiconductor
light source, that is to say in particular by means of the
relationship Pe=UI.
[0032] In various embodiments, the electrical power Pe impressed
into the at least one semiconductor light source has been purged of
any electrical power impressed into an electronic unit possibly
present, for example by forming the difference between (measured)
electrical power impressed into the entire lighting device minus
the (previously known or measured) electrical power impressed into
the electronic unit. This may be advantageous in various
embodiments if a measurement of the electrical power is carried out
on a common electrical line or on the lighting device as such.
[0033] Alternatively, an electrical power of the electronic unit
possibly present may be disregarded, for example if the measurement
of the electrical power Pe is carried out (e.g. by means of a
voltage measurement) only on the at least one semiconductor light
source and/or if the electrical power of the electronic unit is
comparatively low.
[0034] In various embodiments, the electric current I impressed
into the at least one semiconductor light source is constant. This
may be achieved for example by means of a current stabilizer
circuit. This affords the advantage that the electrical power Pe
can be determined by means of a simple voltage measurement and can
be regulated or set by means of a single voltage regulation. The
current I may be set or regulated in particular to a predetermined,
in particular variable, desired value.
[0035] In one configuration, moreover, determining the light power
is followed by a step of varying or changing the electrical power
for setting the light power to a predetermined (desired or normal)
value or range of values. As a result, a light power can be kept
constant or at least in a predetermined range over a lifetime of
the at least one semiconductor light source. As a result, in turn,
when a lighting device is present which includes semiconductor
light sources which emit light of different colors for forming a
mixed light, a cumulative color locus of the mixed light can be
kept constant or in a predetermined range, if appropriate with
total light power or brightness changed in a targeted manner
("color locus calibration").
[0036] In one configuration, generally, the method is carried out
for a plurality of groups of semiconductor light sources, e.g.
emitting in different colors. The plurality of groups of
semiconductor light sources may include light emitting diodes
(LEDs), for example, which emit light colored red, green and/or
blue. Alternatively, it is possible for example to calibrate groups
of semiconductor light sources which emit greenish-white (mint)
light and/or amber light, if appropriate additionally with at least
one LED that emits red or orange light, e.g. in the context of the
"Brilliant Mix" concept from OSRAM Opto Semiconductors GmbH. This
configuration generally makes it possible to keep a cumulative
color locus of the mixed light constant or in a predetermined
range, if appropriate with total light power or brightness changed
in a targeted manner. In order to carry out the method among a
plurality of groups of semiconductor light sources, it may be
applied to said groups successively, in various embodiments.
[0037] Generally, a calibration or implementation of the method may
be performed on the basis of a brightness determined from the light
power and assessed by eye. For this purpose, the step of
determining the light power may be followed by a step of
determining the eye-assessed brightness from the light power, e.g.
by means of a corresponding characteristic curve or table.
[0038] In one development, the method is initiated independently by
the lighting device, e.g. at predetermined intervals in an
operating period (e.g. every one thousand hours), after a
switch-on, on a predetermined date, etc.
[0039] In an additional or alternative development the method is
initiated externally, for example is triggered manually (e.g. by
means of a corresponding switch) or by an external control command
(e.g. via a DALI or DMX connection), but is carried out as such by
the lighting device.
[0040] Generally, this method may be combined with a further method
which compensates for a different temperature dependence of the
brightness of semiconductor light sources emitting light in
different colors (e.g. with an InGaAlP chip and/or InGaN chip),
e.g. between a switch-on instant and a thermally compensated or
settled state.
[0041] Various embodiments provide a lighting device including at
least one semiconductor light source, wherein the lighting device
is designed for carrying out the method as described above. The
lighting device may be embodied analogously to the method and have
the same advantages.
[0042] The lighting device may include for this purpose in various
embodiments a (at least one) voltage measuring device and a (at
least one) temperature measuring device.
[0043] In one configuration, the lighting device is designed for
independently carrying out the method and includes for this purpose
a correspondingly designed electronic control unit, e.g.
driver.
[0044] Alternatively or additionally, the lighting device may be
designed for carrying out the method (in a distributed manner)
together with an external control device.
[0045] The lighting device may be for example a luminaire, a lamp
or a lighting module.
[0046] Various embodiments provide a system including at least one
lighting device as described above and including an external
control device, wherein the system is designed for carrying out the
method as described above in a manner distributed with respect to
said system. This enables a simpler and less expensive lighting
device. Moreover, this makes it possible, in a simple manner, to
coordinate a light emission of a plurality of luminaires with one
another, e.g. with regard to a brightness or a color locus.
[0047] The FIGURE shows a lighting device in the form of a
luminaire 11 including a plurality of semiconductor light sources
in the form of LEDs 12, 13, 14, The LEDs 12-14 here form three
groups of LEDs which emit light of different colors, e.g. a first
group including at least one "red" LED 12, emitting red light, a
second group including at least one "green" LED 13, emitting green
light, and a third group including at least one "blue" LED 14,
emitting blue light. The light from the LEDs 12-14 generates an,
e.g. white, mixed light, the desired cumulative color locus of
which should be complied with as precisely as possible.
[0048] The luminaire 11 includes an electronic control unit 15,
e.g. a driver, which drives the LEDs 12-14 and supplies them with
electrical signals e.g. in a targeted manner. For this purpose, the
electronic control unit 15 has a current stabilizer circuit, such
that the current impressed into the groups of LEDs 12-14 is at
least substantially constant, that is to say I=const. holds true.
In this case, the current for different groups of LEDs 12-14 can be
identical (e.g. in the case of the series connection thereof) or
different (e.g. in the case of the parallel connection
thereof).
[0049] The LEDs 12-14 and the electronic control unit 15 are
arranged on a common cooling body (not illustrated). The cooling
body has, in particular, a thermal resistance that is practically
constant for the operation of the luminaire 11.
[0050] The luminaire 11 furthermore includes at least one, in
various embodiments exactly one, voltage measuring device 16 for
measuring a voltage U present at the respective groups of LEDs
12-14.
[0051] The luminaire 11 also includes at least one temperature
measuring device 17, e.g. including at least one temperature
sensor, for measuring S2 a temperature T present at the groups of
LEDs 12-14. The luminaire 11 may include for example exactly one
temperature measuring device 17, in particular since the groups of
LEDs 12 to 14 are fitted on a common cooling body (not
illustrated). On the cooling body, the temperature T of the LEDs
12-14 may also be sensed by means of the temperature measuring
device 17.
[0052] When the luminaire 11 is switched on, in order to carry out
the method, firstly a step S1 involves measuring an associated
temperature T0 and then, e.g. after a few minutes, a temperature Tb
in a thermally settled state of a currently selected group of LEDs
12-14. Moreover, e.g. at the same time as or with a small distance
of time with respect to the temperature Tb, the voltage U present
at the group of LEDs 12-14 currently under consideration is
measured in a step S2.
[0053] In a step S3, the electronic control unit 15 determines
therefrom the thermal power loss Pth of the currently selected
group of LEDs 12-14 in accordance with Pth=(Tb-T0)/Rth=.DELTA.T/Rth
(where Rth is previously known or determined in situ). If an
influence of an electronic unit, e.g. the electronic control unit
15, is present during a measurement of the temperature Tb in step
S2, in a step S4 it is possible to subtract its electrical power
corresponding to its thermal power loss.
[0054] In a step S5, furthermore, for the group of LEDs 12-14
currently under consideration, the electrical power thereof Pe=UI
is determined by means of the electronic control unit 15, where I
is assumed to be constant (arbitrarily settable, but then chosen to
be fixed).
[0055] From Pth and Pe, in a step S6 the light power Pl of the
group of LEDs 12-14 under consideration is determined in accordance
with Pl=Pe-Pth by means of the electronic control unit 15.
[0056] In a subsequent step S7, by means of the electronic control
unit 15, a deviation of the light power Pl determined from a
desired light power is determined and the power Pe applied to the
group of LEDs 12-14 currently under consideration is readjusted in
the event of a deviation. The luminaire 11 is therefore configured
for automatically carrying out method steps S1 to S7. The method
may be initiated internally, e.g. by means of a rule stored in the
electronic control unit 15. Alternatively or additionally, the
electronic control unit 15 may be communicatively connected to an
external control device 18, via which it receives a command for
initiating the method.
[0057] Steps S1 to S7 are carried out successively for each of the
groups of LEDs 12-14. The initial temperature T0 at the common
cooling body is the same for all groups of LEDs 12-14 and therefore
need only be measured once. The thermal power loss of the
electronic control unit 15 is subtracted each time. In various
embodiments, itIt is provided to measure the thermal power loss of
the electronic control unit 15 for this purpose since it can be
different depending on the operation of the groups of LEDs
12-14.
[0058] Although the invention has been more specifically
illustrated and described in detail by means of the exemplary
embodiment shown, the invention is nevertheless not restricted
thereto, and other variations can be derived therefrom by a person
skilled in the art, without departing from the scope of protection
of the invention.
[0059] In this regard, the method may proceed at least in part (in
a distributed manner) also on a system including at least one
luminaire 11 and including the eternal control device 18 (e.g. a
DMX or DALI control device). For this purpose, the at least one
luminaire 11 may measure for example the temperature T and the
voltage U analogously to steps S1 and S2, respectively, and
communicate the measured values to the external control device 18,
as indicated by the double-headed arrow. The external control
device 18 may then calculate the light power Pl therefrom and send
corresponding control data for calibrating the LEDs 12 to 14 of the
luminaire 11 to the luminaire 11, e.g. analogously to step S7.
[0060] In general, "a", "one", etc. can be understood to mean a
singular or a plural, in particular in the sense of "at least one"
or "one or a plurality", etc., as long as this is not explicitly
excluded, e.g. by the expression "exactly one", etc.
[0061] Moreover, a numerical indication can encompass exactly the
indicated number and also a customary tolerance range, as long as
this is not explicitly excluded.
LIST OF REFERENCE SIGNS
[0062] 11 Luminaire
[0063] 12 red LED
[0064] 13 green LED
[0065] 14 blue LED
[0066] 15 Electronic control unit
[0067] 16 Voltage measuring device
[0068] 17 Temperature measuring device
[0069] 18 External control device
[0070] Pl Light power
[0071] Pe Electrical power
[0072] Pe; L Electrical power of the luminaire
[0073] Pth Thermal power loss
[0074] S1 Step
[0075] S2 Step
[0076] S3 Step
[0077] S4 Step
[0078] S5 Step
[0079] S6 Step
[0080] S7 Step
[0081] T Temperature
[0082] T0 Temperature at the switch-on instant
[0083] Tb Temperature after thermalization
[0084] U Voltage
[0085] While the invention has been particularly shown and
described with reference to specific embodiments, it should be
understood by those skilled in the art that various changes in form
and detail may be made therein without departing from the spirit
and scope of the invention as defined by the appended claims. The
scope of the invention is thus indicated by the appended claims and
all changes which come within the meaning and range of equivalency
of the claims are therefore intended to be embraced.
* * * * *